1. Field of the Invention
The present invention relates to the technical field of optical materials and devices. In particular, the invention relates to a dye loaded zeolite material; the invention further relates to a pigment material, a luminescent optical device, an optical sensor device, a light emitting device and a photonic energy harvesting device, all the aforesaid said comprising a dye loaded zeolite material.
2. Description of the Prior Art
The structural, morphological, physical, and chemical variety of zeolites has led to applications in different fields like catalysis, ion exchange, membranes, and chemical sensors where dynamic processes involving ions or adsorbate molecules play an important role (Thomas, J. M. Spektrum der Wissenschaft, June 1992, 88). Situations where the zeolites mainly serve as host for supramolecular organization of molecules, ions, complexes and clusters to prepare materials with new properties such as non-linear optical (Cox, S. D.; Gier, T. E.; Stucky, G. D. Chem. Mater. 1990, 2, 609), quantum-size (Stucky, G. D.; MacDougall, J. E. Science 1990, 247, 669; Brühwiler, D.; Seifert, R.; Calzaferri, G. J. Phys. Chem B 1999, 103, 6397), micro laser (Vietze, U.; Krauss, O.; Laeri, F.; Ihnlein, G.; Schüth, F.; Limburg, B.; Abraham, M. Phys. Rev. Lett. 1998, 81, 4628) and artificial antenna characteristics are new fields of growing interest (Wöhrle, D.; Schulz-Ekloff, G. Adv. Mater. 1994, 6, 875; Schüth, F. Chemie in unserer Zeit 1995, 29, 45; Ozin, G. A.; Kuperman, A.; Stein, A. Angew. Chem 1989, 101, 373.).
Some of these new materials can be considered as static and stable arrangements of guests in the zeolite host under a broad range of conditions (Lainé, P.; Lanz, M.; Calzaferri, G. Inorg. Chem. 1996, 35, 3514). In other cases, however, the adsorption, desorption or ion exchange of molecules or ions are reversible processes which lead to a wide range of phenomena (Seifert, R.; Kunzmann, A.; Calzaferri, G. Angew. Chem. Inst. Ed. 1998, 37, 1521; Brühwiler, D.; Gfeller, N.; Calzaferri, G. J. Phys. Chem, B 1998, 102 ,2923; Ramamurthy, V.; Sanderson, D. R.; Eaton, D. F. J. Am. Chem. Soc. 1993, 115, 10438.).
Plants are masters of efficiently transforming sunlight into energy. In this process, every plant leaf acts as a photonic antenna system, wherein photonic energy in the form of sunlight is transported by chlorophyll molecules for the purpose of energy transformation. Accordingly, the synthesis, characterization and possible application of an artificial photonic antenna for harvesting light within a certain volume and for transport of the resultant electronic excitation energy to a specific location of molecular size has been the target of research of several laboratories. Imaginative attempts to build an artificial photonic antenna have been reported, including multinuclear luminescent metal complexes, multichromophore cyclodextrines, Langmuir-Blodgett films, and dyes in polymers. Sensitization processes in silver halide photographic materials as well as the spectral sensitization of semiconductor oxides also bear in some cases aspects of artificial photonic antenna systems (“Energy Migration in Dye-Loaded Hexagonal Microporous Crystals”, Gfeller, N.; Calzaferri, G,. J. Phys. Chem. B 1997, 101, 1396-1408 and references cited therein).
However, to our knowledge, the system reported by us in “Fast Energy Migration in Pyronine-Loaded Zeolite L Microcrystals”, Gfeller, N.; Megelski, S.; Calzaferri, G. J. Phys. Chem B 1999, 103, 1250-1257, is the first artificial photonic antenna that works well enough to deserve this name. In this artificial system, zeolite cylinders are adopted for forming a bidirectional photonic antenna wherein the light transport is made possible by specifically organized dye molecules that mimic the natural function of chlorophyll. Zeolites are materials with different cavity structures. Some of them occur in nature as a component of the soil. We use zeolite L crystals of cylindrical morphology which consist of a continuous channel system and we have succeeded in filling each individual channel with chains of joined but noninteracting dye molecules. Light shining on the cylinder is first absorbed and the energy is transported by the dye molecules inside the channels to the cylinder ends (J. Phys. Chem. B 1997, 101, 1396-1408; “Transfer of Electronic Excitation Energy between Dye Molecules in the Channels of Zeolite L”, Gfeller, N.; Megelski, S.; Calzaferri, G. J. Phys. Chem B 1998, 102, 2433-2436; “Zeolite Microcrystals as Hosts for Supramolecular Organization of Dye Molecules”, Calzaferri, G. Chimia 1998, 52, 525-532; “Fast Energy Migration in Pyronine-Loaded Zeolite L Microcrystals”, Gfeller, N.; Megelski, S.; Calzaferri, G. J. Phys. Chem B 1999, 103, 1250-1257; “Dye Molecules in zeolite L nano crystals for efficient light harvesting”, Calzaferri, G. in Photofunctional Zeolites, Nova Science Publishers NY, Editor. M. Anpo, 2000, 205-218; Pauchard, M.; Deveaux, A.; Calzaferri, G. “Dye-Loaded Zeolite L Sandwiches”, CHEMISTRY a Eur. J. 2000, 6, 3456-3470). 
We have previously synthesized nanocrystalline zeolite L cylinders ranging in length from 300 nm to about 3000 nm. A cylinder of 600 nm consists of, for example, about 100'000 channels arranged essentially parallel to each other. A typical zeolite L material of this kind is shown in FIG. 1. Single molecules of the luminescent dye oxonine, which is capable of emitting light in the red wavelength range, were inserted into ends of the zeolite's channels that had previously been filled with the luminescent dye pyronine, which is capable of emitting light in the green wavelength range. By means of this arrangement, experimental proof was furnished that efficient light transport is possible in such zeolite systems. Light of appropriate wavelength impinging on the zeolite is absorbed by pyronine molecules only. After such an absorption process, the energy moves along the molecules in the zeolite channel until it reaches a terminal oxonine molecule. The oxonine absorbs the energy by a radiationless energy transfer process, but is not able to send the energy back to the pyronine. Instead, it emits the energy in the form of red light, visible to the naked eye.
We have developed two methods for preparing suitable dye loaded zeolite materials, one method working at a solid/liquid interface and the other method working at a solid/gas interface. Other approaches for preparing similar materials are in situ and crystallization inclusion synthesis. In our previous work, cationic dyes have been inserted into the channels of zeolite L via ion exchange from a suspension, thus leading to zeolite L materials with donor molecules located in the middle and acceptor molecules at the channel ends. After selective electronic excitation of the donor molecules, fast energy migration along the c-axis and energy transfer at the channel ends to the acceptor molecules was observed. Subsequently, we have succeeded in preparing three-dye-loaded zeolite L sandwiches. The general concept of the preparation method of these materials is illustrated in FIG. 2 and a selection of molecules that have been studied is given in FIG. 3. First, a neutral dye molecule is inserted e.g. from the gas phase, filling the channels to the desired degree. Provided that the inserted molecules are not rapidly displaced by water, this material can then be ion exchanged with a second dye. This can be well controlled, so that a specifically desired space is left for the third dye, which is either inserted in a next ion exchange process, or from the gas phase. We have shown that by these means a bidirectional antenna for light collection and transport can been prepared so that the whole light spectrum can be used, transporting light energy from blue to green to red.
Within the context of this work several reactions and equilibria play a role and have been discussed: Insertion reaction of neutral dyes, adsorption at the outer surface, hydration, displacement and reinsertion reactions, and cation exchange. Many data have been obtained for p-terphenyl (pTP). The size of pTP and its chemical properties make it an excellent model for studying relevant parameters and for developing new preparation methods. The first bi-directional three-lye-zeolite L sandwich antenna has been realized with DPH as first luminescent dye. We have observed that the energy of near UV light that is absorbed in the middle part of the antenna by DPH is transferred to adjacent pyronine molecules, i.e. to the second luminescent dye, along which it migrates until it reaches the pyronine/oxonine interface, where a further energy transfer occurs from pyronine to oxonine, i.e. to the third luminescent dye (Calzaferri, G.; Brühwiler, D.; Megelski, S.; Pfenniger, M.; Pauchard, M.; Hennessy, B.; Maas, H.; Déveaux, A.; Graf, U. “Playing with Dye Molecules at the Inner and Outer Surface of Zeolite L”, Solid State Sciences, 2000, Volume 2, 421-447, incorporated herein by reference).
Beyond being usable for a light harvesting system, the principles described are expected to be exploitable in numerous other applications. However, the dye loaded zeolite materials and any devices made thereof that have so far been described, exhibit a number of significant shortcomings and disadvantages. In particular, the stability of such systems is still unsatisfactory, mainly because of an undesirable migration of the luminescent dye molecules out of the zeolite channels resulting in a depletion of the dye loaded zeolite material.
Moreover, the tasks of external trapping of excitation energy or—conversely—of injecting energy at a specific point of the photonic antenna, the realization of a mono-directional photonic antenna and the coupling of such photonic antennae to specific devices have not been solved so far.